This invention relates to a method and apparatus for manufacturing a gas displacement pressurized packaging body in containers such as cans for canned goods, molded containers, plastic bottles, and glass bottles, etc., and more particularly to a method and apparatus for manufacturing a pressurized packaging body wherewith the inert gas displacement ratio can be increased, container internal pressures can be stably obtained that are suitable positive pressures, small volume injecting of a liquid inert gas can be done with high precision, and low pressurized packaging bodies can be obtained which exhibit outstanding guaranteed quality.
Conventionally, in manufacturing canned goods, a pressurized canned goods manufacturing method is commonly employed wherein the head space of the can is injected with an inert gas (which is ordinarily liquid nitrogen and therefore hereinafter represented by liquid nitrogen) that is made to flow down while the can is being conveyed from the filler to the seamer, and the can is seamed and sealed while the vaporizing expansion of the liquid nitrogen is continuing, whereby an internal pressure is produced by the vaporizing expansion of remaining liquid nitrogen after sealing. The main objective in injecting the liquid nitrogen and causing a positive pressure to be generated in the can is to give rigidity to the can by the positive pressure, thus making it possible to use thinner walled materials for the can and to reduce the amount of material used. Moreover, by displacing the gas (air) inside the can with nitrogen (inert gas) and removing the oxygen, the benefit of preventing flavor deterioration due to oxidation of the contents is also gained. Another objective is to aggressively make the pressure inside the can either positive or negative, and then perform an inspection to determine whether the pressure inside the can is being held at a prescribed pressure or not, thereby making it possible to detect leakage of the canned goods and spoilage in the contents due to bacterial incursion, and hence to guarantee that the contents are safe.
However, with the conventional method wherein liquid nitrogen is sealed in and an internal pressure is produced, there is a drawback that fluctuation of the injected liquid nitrogen volume is significant and the prescribed internal pressure can not be stably obtained, particularly because the liquid nitrogen splashes out to the outside of the can during liquid nitrogen injection and during lid seaming. For that reason, there is a problem that the material used for the can cannot be made thin to the limit of what can withstand the prescribed internal pressure, and the quantity of material used cannot be reduced effectively. When a small volume of liquid nitrogen is injected, in order to obtain low internal pressure cans, the fluctuation relative to the target injecting volume becomes significantly larger, wherefore it has not been possible to stably obtain low pressurized cans by injecting small volumes of liquid nitrogen with the conventional liquid nitrogen injection method. In the case of easily spoilable liquid content such as beverages containing milk, vacuum cans or low pressurized cans are demanded wherewith it is easy to detect swelling caused by microorganisms. However, when the internal pressure fluctuation is significant as described above, it can no longer be determined whether swelling is caused by microorganisms or by fluctuation in internal pressure resulting from liquid nitrogen injection. For that reason, until now, the easily spoilable liquid content have had to fill with thick walled cans because means for enhancing can strength by producing a pressure inside the cans by injecting liquid nitrogen could not be employed.
Furthermore, with the conventional liquid nitrogen injection method, internal pressure fluctuation in pressurized cans also happens as a result of the fluctuation in the amount of filling contents. That is, even supposing that the definite volume of liquid nitrogen remains, when the volume of filling contents increases (that is, the head space decreases), the internal pressure increases due to vaporizing expansion of the liquid nitrogen. Therefore, in order to obtain accurate internal pressure, the liquid nitrogen injection volume must be controlled according to the fluctuation of the filling content volume. It has been impossible to achieve this with the conventional method.
It has also been proposed that the liquid nitrogen be atomized and then injected (Japanese Patent Publication No. S59-9409/1984). However, unlike with ordinary liquids having a high boiling point, liquid nitrogen that have a boiling point of xe2x88x92196xc2x0 C. at atmospheric pressure and vaporizes very easily, atomization cannot be done stably even when it is sprayed under pressure, wherefore this method has not yet been made practical. The cause for this is that, when liquid nitrogen is sprayed to the atmosphere, the liquid nitrogen is heated and vaporized by the atmosphere at room temperature, whereupon vaporization occurs in the spray nozzle prior to atomization, causing pressure fluctuations and foam gripping at the spray orifice, which causes pulsation. In particular, when spraying is done under high pressure, the boiling point decreasing when the liquid nitrogen is passing through the spray nozzle becomes large, the liquid nitrogen boils inside the nozzle, pulsation occurring, whereupon fine particles cannot be stably obtained. Another cause is that the moisture contained in the atmosphere freezes at the nozzle tip, blocking the spray orifice and resulting in unstable spray volume. Even assuming that stable atomization can be effected, the filling accuracy of the fine particles of liquid nitrogen injected in the container will be poor unless the injected liquid nitrogen spray pattern is consistent with the direction of conveyance. Particularly in the case of a high speed filling line, the fine particles of liquid nitrogen may splash back when colliding the surface of the liquid content so that they splash out of the container. Thus this method still does not satisfy to obtain low pressurized cans that requires the small volume injection of liquid nitrogen with extremely high accuracy.
Therefore, an object of the present invention is to provide a method and apparatus for manufacturing a pressurized packaging body wherewith prescribed internal pressures of the pressurized packaging bodies can be stably obtained even at low internal pressure by increasing the accuracy of the initial internal pressure, and the inert gas displacement ratio in the pressurized packaging bodies can be dramatically improved over the prior art.
A detailed object of the present invention is to provide a method and apparatus for manufacturing a pressurized packaging body, wherewith small volume injection of liquefied inert gas or solidified inert gas can be done precisely by stably made into fine particles, wherewith low pressurized gas displacement packaging bodies are obtained which exhibit outstanding guaranteed quality, and wherewith it is possible to employ thin walled cans even for cans containing low acid beverages.
The present invention, basically, is a method wherewith a liquefied inert gas or solidified inert gas that is to be vaporized to become an inert gas is made into fine particles, sprayed together with a low temperature inert gas having a temperature that is at or below the final equilibrium temperature of the gas displacement pressurized packaging body into the head space of a container filled with contents, and sealed, thereby displacing the gas in the head space with the inert gas, and, at the same time, causing an internal pressure to be produced both by the vaporizing expansion of the fine particles of the remaining liquefied inert gas or the fine particles of the remaining solidified inert gas, and also by the thermal expansion of the said low temperature inert gas, after sealing. Thus it is possible to obtain pressurized packaging bodies that exhibit high internal pressure accuracy and a high inert gas displacement ratio, whereupon the object mentioned above is attained.
The fine particles of the said liquefied inert gas can be definitely generated by supplying a liquefied inert gas from a liquefied inert gas tank to the inlet of the orifice of the said spray nozzle with preventing the vaporization thereof by a thermally insulated passageway, passing through the said orifice in a liquid state and discharging it into the atmosphere, whereupon the liquefied inert gas exhibits a rapid vaporized expansion effect immediately after exiting the orifice, thereby causing the other liquefied inert gas still in the liquid phase to be made into fine particles. Liquid nitrogen is basically adopted as the liquefied inert gas mentioned above and dry ice as the solidified gas, but such are not necessarily limited thereto.
For the said low temperature inert gas, the vaporized gas generated by the vaporization of some part of the liquefied inert gas supplied to the said spray nozzle under prescribed pressure is used, but that may be used in conjunction also with inert gas supplied by a separate passageway from the inert gas supply source. In order to increase the accuracy of injection to the inside of the container, it is preferable that the liquefied gas be sprayed toward the opening of the container from the spray nozzle so that a pattern having a spread angle of from 20xc2x0 to 100xc2x0 is formed. When that is done, the range of spray flow volume for the liquefied gas should be from 0.2 g/s to 4.0 g/s. If the spray flow volume is less than 0.2 g/s, the desired internal pressure of container will not be obtained, whereas if it exceeds 4.0 g/s, pulsation readily occurs during spraying, whereupon the spray angle will not stabilize and it will be difficult to obtain a stable spray flow. A more preferable spray flow volume is the range of 0.2 g/s to 3.0 g/s. Here, the spray pattern means the spatial distribution of numerous fine particles of liquid nitrogen that is formed immediately after discharging from the nozzle orifice. Liquid nitrogen is generally used as the liquefied gas that is injected into the container in order to manufacture a gas displacement pressurized packaging body, and the present invention can also be favorably adapted to liquid nitrogen spray injection.
It is preferable that the spray pattern be formed so that the horizontal cross-sectional shape thereof approximates a shape somewhere between a square and an ellipse so that thereby the inside of the container can be injected with the fine particles of liquefied gas efficiently. The fine particles of the liquefied gas sprayed from the spray nozzle should have a particle diameter of 2 mm or less. When the particle diameter exceeds 2 mm, it is difficult to control injection precisely just as with conventional flow-down injection.
Moreover, in order to make the liquefied gas into fine particles efficiently and definitely, the nozzle temperature while the liquefied gas is being sprayed should be no less than the boiling point of the liquefied gas and no more than that boiling point +75xc2x0 C., and preferably a temperature between that boiling point and the boiling point +50xc2x0 C. When liquid nitrogen is being sprayed, for example, the nozzle temperature should be no greater than xe2x88x92120xc2x0 C. and no less than the boiling point of the liquefied gas, and preferably between xe2x88x92150xc2x0 C. and the boiling point of the liquefied gas. The spray pressure should be from 1 kPa to 150 kPa, and preferably from 1 kPa to 30 kPa.
When the liquefied gas is being atomized, the spray nozzle should be isolated from the outside air by double purge gasses consisting of an inner purge gas at a comparatively low temperature and an outer purge gas at a comparatively high temperature. However, it is also permissible to use only low temperature vaporized gas that is vaporized inside a liquefied gas storage tank, particularly a pressurized liquefied gas storage tank.
It is also desirable that the liquefied gas be sprayed diagonally, at an angle of 5xc2x0 to 45xc2x0, and preferable of 15xc2x0 to 40xc2x0, from the vertical, with respect to the conveyance of the container, so that the liquefied gas spray flow contains a velocity component in the direction of container conveyance. The spray distance from the tip of the spray nozzle to the contents surface of the container should be from 5 to 100 mm, and preferably from 45 to 60 mm. By such means as these, it is possible to stably obtain low pressurized packaging bodies having a container internal pressure of 0.2 to 0.8 kgf/cm2 after sealing.
Basically, when the said container is a metal can, the said liquefied inert gas can be sprayed to inject the can while it is being conveyed from the filler to the seamer. However, by settling the spray nozzle in the seamer as a undercover gassing device, the liquefied inert gas can be sprayed inside the container by undercover gassing method.
The apparatus for manufacturing the pressurized packaging body of the present invention comprises a liquefied inert gas storage tank and spray device that have a spray nozzle deployed so that it is connected to the bottom of that liquefied inert gas storage tank. The spray devices have valve for controlling the liquefied inert gas flow volume, the spray nozzle having nozzle orifice, and a thermally insulated passageway for supplying the liquefied gas from the valve to the nozzle orifice.
The means of vacuum insulating the liquefied inert gas flow passageway or the like may be adopted for the thermally insulated passageway mentioned above. However, said spray nozzle can be cooled and controlled the temperature more effectively by configuring the outer circumference of the liquefied inert gas flow passageway from the said valve to the said spray nozzle by enclosing with a nozzle cooling chamber into which the liquefied inert gas flows from the liquefied inert gas storage tank. The structure of the spray nozzle for making the liquefied inert gas into fine particles more definitely should have a spray nozzle tip or nozzle tips consisting of a small orifice or orifices having an opening area of 0.15 to 4 mm2 and preferably of 0.2 to 3 mm2. If the opening area in the spray nozzle orifice or orifices is smaller than that range, vaporization will occur during discharging and it will be very difficult to achieve atomization, whereas if it is larger that range, the liquid droplets will become too large, similar to a flow-down injection situation, and it will become difficult to obtain fine particles.
It is desirable to deploy the said spray nozzle inclined at an angle of 5xc2x0 to 45xc2x0, and preferably of 15xc2x0 to 40xc2x0, from the vertical downward direction, gives the spray flow a velocity component in the direction of container conveyance so that the fine particles of the liquefied gas impacts softly on the liquid surface inside the container. It is preferable that the said spray means comprise purge device for preventing frosting by isolating at least the vicinity of the nozzle outlets from the outside air by a purge gas. These said purge gas device are formed as a double purge gas hood arrangement consisting of an inner purge gas hood forming an inner purge gas passageway and an outer purge gas hood forming an outer purge gas passageway. Moreover, the part facing the nozzle tip of said inner purge gas hood can be configured as a spray beak by forming the said inner purge gas hood to enclose from the lower outer circumference part to the nozzle tip of the said spray body. However, when the vaporized gas in the inert gas storage tank, and particularly the vaporized gas generated from a pressurized tank, is inducted as the purge gas, it is possible to obtain low temperature purge gas with sufficient volume for adequate purging without forming double purge passageways, making the structure simpler.
Spray device is desirable to configure a spray device assembly by attaching each constituent parts so that the assembly process can be simplified. Also, by either deploying the said spray devices in a plurality along with the direction of container conveyance at the bottom of the liquefied gas storage tank, or deploying those in combination with liquefied gas flow-down devices to configure multiple nozzles, it is possible to decrease fluctuation relative to internal pressure and to effect more precise injection, so that is desirable. It then also becomes possible to effect highly precise liquefied gas injection even when the spray volume is large. If an initial purge mechanism for supplying a dry heated gas to the inside of the liquefied gas storage tank, prior to supplying the liquefied gas, and removing moisture from the tank inside is connected to the liquefied gas storage tank, an initial purge can be performed and no frost will form in the tank, so that is desirable.